U.S. patent application number 14/686061 was filed with the patent office on 2015-08-06 for methods of securing one or more optical fibers to a ferrule.
The applicant listed for this patent is CORNING OPTICAL COMMUNICATIONS LLC. Invention is credited to Jeffrey Dean Danley, Robert Bruce Elkins, II, Thomas Dale Ketcham, Darrin Max Miller, Robert Michael Morena.
Application Number | 20150219860 14/686061 |
Document ID | / |
Family ID | 53754698 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150219860 |
Kind Code |
A1 |
Danley; Jeffrey Dean ; et
al. |
August 6, 2015 |
METHODS OF SECURING ONE OR MORE OPTICAL FIBERS TO A FERRULE
Abstract
A method of securing an optical fiber to a ferrule involves
heating the ferrule to cause thermal expansion. A ferrule bore of
the ferrule increases in diameter as a result of the thermal
expansion, and an optical fiber is inserted into the ferrule bore.
The ferrule is then cooled so that the ferrule bore decreases in
diameter and forms a mechanical interface with the optical fiber.
Finally, the optical fiber is fused to the ferrule by irradiating
the optical fiber and the ferrule with laser energy.
Inventors: |
Danley; Jeffrey Dean;
(Hickory, NC) ; Elkins, II; Robert Bruce;
(Hickory, NC) ; Ketcham; Thomas Dale; (Horseheads,
NY) ; Miller; Darrin Max; (Hickory, NC) ;
Morena; Robert Michael; (Lindley, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING OPTICAL COMMUNICATIONS LLC |
Hickory |
NC |
US |
|
|
Family ID: |
53754698 |
Appl. No.: |
14/686061 |
Filed: |
April 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US14/69223 |
Dec 9, 2014 |
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14686061 |
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PCT/US13/63998 |
Oct 9, 2013 |
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PCT/US14/69223 |
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61917765 |
Dec 18, 2013 |
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61716815 |
Oct 22, 2012 |
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Current U.S.
Class: |
156/66 |
Current CPC
Class: |
G02B 6/3855 20130101;
B29C 65/16 20130101; G02B 6/32 20130101; G02B 6/3854 20130101 |
International
Class: |
G02B 6/38 20060101
G02B006/38 |
Claims
1. A method of securing an optical fiber to a ferrule, comprising:
heating the ferrule to cause thermal expansion, wherein a ferrule
bore of the ferrule increases in diameter as a result of the
thermal expansion; inserting the optical fiber into the ferrule
bore; cooling the ferrule after thermal expansion and after
inserting the optical fiber into the ferrule bore so that the
ferrule bore decreases in diameter and forms a mechanical interface
with the optical fiber; and fusing the optical fiber to the ferrule
by irradiating the optical fiber and the ferrule with laser
energy.
2. A method according to claim 1, wherein heating the ferrule to
cause thermal expansion comprises irradiating the ferrule with
laser energy.
3. A method according to claim 2, wherein at least one common laser
source is used to heat the ferrule to cause thermal expansion and
to fuse the optical fiber to the ferrule, the method further
comprising: changing at least one optical delivery property of the
at least one common laser source after heating the ferrule and
before fusing the optical fiber to the ferrule.
4. A method according to claim 3, wherein inserting the optical
fiber into the ferrule bore comprises extending an end portion of
the optical fiber beyond a front end face of the ferrule, the
method further comprising: operating the at least one common laser
source to form an optical surface on the end portion of the optical
fiber after extending the end portion of the optical fiber beyond
the front end face of the ferrule.
5. A method according to claim 4, wherein the at least one common
laser source is operated to form the optical surface on the end
portion of the optical fiber after fusing the optical fiber to the
ferrule.
6. A method according to claim 5, wherein before operating the at
least one common laser source to form the optical surface but after
fusing the optical fiber to the ferrule, the method further
comprises: changing at least one optical delivery property of the
at least one common laser source.
7. A method according to claim 1, wherein the optical fiber is only
fused to the ferrule at locations at spaced least 1 mm from a front
end face of the ferrule.
8. A method according to claim 1, further comprising: providing the
ferrule, wherein the ferrule is comprised of an inorganic composite
material having a material gradient in a radial direction from at
least 75% by volume of a first inorganic material to at least 75%
by volume of a second inorganic material.
9. A method according to claim 8, wherein the first inorganic
material comprises a ceramic and the second inorganic material
comprises silica.
10. A method according to claim 9, wherein the ceramic material of
the ferrule comprises alumina or zirconia.
11. A method according to claim 8, wherein the first inorganic
material of the ferrule has a fracture toughness of at least 1
MPam.sup.1/2, and further wherein the second inorganic material of
the ferrule has a softening point less than 1000.degree. C.
12. A method according to claim 8, wherein the ferrule includes a
region extending along at least 1/10 of the length of the radius of
the ferrule, and further wherein the material gradient is located
within said region.
13. A method according to claim 12, wherein the material gradient
of the ferrule is continuous over the region of the ferrule.
14. A method according to claim 1, wherein cooling the ferrule
after thermal expansion further comprises forming the mechanical
interface between the ferrule bore and optical fiber along an
entire length of the ferrule bore.
15. A method according to claim 1, further comprising: providing
the ferrule, wherein the ferrule has a coefficient of thermal
expansion at least 15 times greater than a coefficient of thermal
expansion of the optical fiber.
16. A method according to claim 1, further comprising: providing
the ferrule, wherein the ferrule bore defines an interior of the
ferrule and the ferrule further includes an exterior, and wherein
material of the ferrule includes one or more components and is such
that the material changes in thermal expansion coefficient from the
interior to the exterior of the ferrule, wherein the material of
the ferrule between the interior and exterior comprises has an
average thermal expansion coefficient greater than the thermal
expansion coefficient of the interior of the ferrule and less than
the thermal expansion coefficient of the exterior of the
ferrule.
17. The method of claim 16, wherein the thermal expansion
coefficient of the material changes by way of discrete layers in
the material between the interior and exterior of the ferrule.
18. The method of claim 17, wherein the layers are graded such that
each outwardly adjoining layer has a greater thermal expansion
coefficient.
19. The method of claim 17, wherein the ferrule comprises at least
three discrete layers.
20. The method of claim 16, wherein the material of the ferrule is
such that the thermal expansion coefficient transitions from less
than 30.times.10-7/.degree. C. at the interior of the ferrule to
greater than 70.times.10-7/.degree. C. at the exterior of the
ferrule.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of International
Application No. PCT/US2014/069223, filed on Dec. 9, 2014, which
claims the benefit of priority to U.S. Provisional Patent
Application No. 61/917,765, filed on Dec. 18, 2014, both
applications being incorporated herein by reference. This
application is also a continuation-in-part of International
Application No. PCT/US2013/063998, filed on Oct. 9, 2013, which
claims the benefit of priority to U.S. Provisional Patent
Application No. 61/716,815, filed on Oct. 15, 2012, both
applications being incorporated herein by reference.
BACKGROUND
[0002] The disclosure relates generally to optical fibers and more
particularly to methods of securing one or more optical fibers to a
ferrule of a fiber optic connector.
[0003] Optical fibers are useful in a wide variety of applications,
including the telecommunications industry for voice, video, and
data transmissions. In a telecommunications system that uses
optical fibers, there are typically many locations where fiber
optic cables that carry the optical fibers connect to equipment or
other fiber optic cables. To conveniently provide these
connections, fiber optic connectors are often provided on the ends
of fiber optic cables. The process of terminating individual
optical fibers from a fiber optic cable is referred to as
"connectorization." Connectorization can be done in a factory,
resulting in a "pre-connectorized" or "pre-terminated" fiber optic
cable, or the field (e.g., using a "field-installable fiber optic
connector).
[0004] Regardless of where installation occurs, a fiber optic
connector typically includes a ferrule with one or more bores that
receive one or more optical fibers. The ferrule supports and
positions the optical fiber(s) with respect to a housing of the
fiber optic connector. Thus, when the housing of the fiber optic
connector is mated with another fiber optic connector or adapter,
an optical fiber in the ferrule is positioned in a known, fixed
location relative to the housing. This allows an optical connection
to be established when the optical fiber is aligned with another
optical fiber provided in the mating component (the other fiber
optic connector or adapter).
[0005] To minimize signal attenuation through such an optical
connection, the optical fiber should not move relative to the
ferrule. Doing so might alter the precise spatial relationship of
the optical fiber and ferrule and, in turn, affect alignment/mating
with the optical fiber of the mating component. Conventional
methods of preventing movement involves bonding the optical fiber
in a bore of the ferrule with an epoxy-based adhesive ("epoxy").
Although relatively inexpensive, epoxy presents several challenges.
For example, epoxy can be difficult to apply uniformly to all
ferrules such that the quality of adhesive bond may vary. The
spatial relationship of the optical fiber relative to the ferrule
may then be difficult to predict. The need for precise mixing, a
limited pot life after mixing, and long cure times after
application are other challenges that epoxy typically presents.
SUMMARY
[0006] Methods of securing an optical fiber to a ferrule are
described below. The optical fiber could be a single optical fiber
or one of several optical fibers, as may be the case for a
multi-fiber connector, to be secured to the ferrule. Thus, "an
optical fiber" refers to at least one optical fiber. According to
one embodiment, the method involves heating the ferrule to cause
thermal expansion. A ferrule bore of the ferrule increases in
diameter as a result of the thermal expansion, and an optical fiber
is inserted into the ferrule bore. The ferrule is then cooled so
that the ferrule bore decreases in diameter and forms a mechanical
interface with the optical fiber. Finally, the optical fiber is
fused to the ferrule by irradiating the optical fiber and the
ferrule with laser energy.
[0007] Another embodiment involves the same steps mentioned above,
but specifically involves heating the ferrule with at least one
laser to cause the thermal expansion. The at least one laser is
also what is used to irradiate the optical fiber and the ferrule
with laser energy to fuse the optical fiber to the ferrule.
However, fusing may be performed after changing at least one
optical delivery property of the at least one laser.
[0008] Additional features and their advantages will be set forth
in the detailed description which follows, and in part will be
readily apparent to those skilled in the art from the description
or recognized by practicing the embodiments as described in the
written description and claims hereof, as well as the appended
drawings.
[0009] It is to be understood that both the foregoing general
description and the following detailed description are merely
exemplary, and are intended to provide an overview or framework to
understand the nature and character of the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The accompanying drawings are included to provide a further
understanding, and are incorporated in and constitute a part of
this specification. The drawings illustrate one or more
embodiment(s), and together with the description serve to explain
principles and operation of the various embodiments. Persons
skilled in the technical field of optical connectivity will
appreciate how features and attributes associated with embodiments
shown in one of the drawings may be applied to embodiments shown in
others of the drawings.
[0011] FIG. 1 a cross-sectional view of an example of a fiber optic
connector having a ferrule to which an optical fiber is secured
according to methods of the present disclosure;
[0012] FIG. 2 is a perspective view of the ferrule of FIG. 1;
[0013] FIG. 3 is a front elevation view of the ferrule of FIG.
1;
[0014] FIG. 4 is a schematic side view of a fiber optic cable that
includes the optical fiber of FIG. 1;
[0015] FIG. 5 is a cross-sectional view taken along lines 5-5 in
FIG. 4;
[0016] FIG. 6 is a cross-sectional view taken along lines 6-6 in
FIG. 4;
[0017] FIG. 7A is a schematic view of the ferrule of FIGS. 1-3
adjacent to the optical fiber of FIGS. 4-6, wherein the ferrule is
shown as a cross-section taken along line 7A-7A in FIG. 3;
[0018] FIG. 7B is a schematic view similar to FIG. 7A, but further
illustrating the ferrule being heated as part of a method according
to the present disclosure to cause thermal expansion;
[0019] FIG. 7C is a schematic view similar to FIGS. 7A and 7B, but
further illustrating the optical fiber being inserted into the
ferrule;
[0020] FIG. 7D is a schematic view similar to FIGS. 7A-7C, but
further illustrating the ferrule forming a mechanical interface
with the optical fiber after the optical fiber has been inserted
into the ferrule;
[0021] FIG. 8 is a schematic view of a ferrule being heated with a
laser to cause thermal expansion;
[0022] FIG. 9 is a schematic view of a ferrule being heated in an
oven to cause thermal expansion;
[0023] FIG. 10 is a schematic view of a ferrule being induction
heated by an electromagnet to cause thermal expansion;
[0024] FIG. 11 is a schematic side view of a ferrule being
irradiated with laser energy according to a method of the present
disclosure to fuse an optical fiber to the ferrule;
[0025] FIGS. 12 and 13 are schematic side and front views of a
ferrule being irradiated with laser energy according to another
method of the present disclosure to fuse an optical fiber to the
ferrule; and
[0026] FIG. 14 is a graph of an exemplary material gradient profile
for a ferrule used in methods according to the present
disclosure.
[0027] FIG. 15 is a schematic diagram of ferrule in cross-section
according to another embodiment of this disclosure.
[0028] FIG. 16 is a scanning electron microscope (SEM) micrograph
of four sintered layers with a composition gradient according to an
exemplary embodiment.
[0029] FIG. 17 is an SEM micrograph of a silica rod in a material
including 50% glass and 50% glass-ceramic according to an exemplary
embodiment.
[0030] FIGS. 18 and 19 are plots of estimated macro-stresses in
five-layer ferrules according to exemplary embodiments.
[0031] FIGS. 20 and 21 are plots of estimated macro-stresses in
two-layer ferrules.
[0032] FIGS. 22-30 are SEM micrographs showing material
microstructure according to exemplary embodiments.
[0033] FIG. 31 is a schematic diagram of multi-fiber ferrule in
cross-section according to an exemplary embodiment.
DETAILED DESCRIPTION
[0034] Various embodiments will be further clarified by examples in
the description below. In general, the description relates to
methods of securing an optical fiber in a ferrule of a fiber optic
connector. The methods may be part of a cable assembly process for
a fiber optic cable. That is, the methods may be part of
terminating one or more optical fibers from a fiber optic cable
with a fiber optic connector to form a cable assembly. One example
of a fiber optic connector ("connector") 10 for such a cable
assembly is shown in FIG. 1. Although the connector 10 is shown in
the form of a SC-type connector, the methods described below may be
applicable to processes involving different fiber optic connector
designs. This includes ST, LC, FC, MU, and MPO-type connectors, for
example, and other single-fiber or multi-fiber connector
designs.
[0035] Referring FIGS. 1-3, the connector 10 includes a ferrule 12
having a first end 14 and a second end 16, a ferrule holder 18
having opposed first and second end portions 20, 22, and a housing
24. The second end 16 of the ferrule 12 is positioned in the first
end portion 20 of the ferrule holder 18 while the first end 14 of
the ferrule 12 remains outside the ferrule holder 18. The ferrule
holder 18 may comprise, for example, a plastic material molded over
the second end 16 of the ferrule 12, which may in turn comprise a
ceramic material, such as zirconia. Other details related to
possible constructions/compositions of the ferrule 12 and
pertaining methods of the present disclosure will be set forth
below. In embodiments where the ferrule holder 18 is molded, a
notch 26 may be provided in the ferrule 12 so that a portion 28 of
the ferrule holder 18 is disposed in the notch 26 to help prevent
the ferrule 12 from disengaging with the ferrule holder 18. In
alternative embodiments, the ferrule 12 may simply be press-fit
into the ferrule holder 18, which may or may not be a molded
component.
[0036] The ferrule 12 also includes a ferrule bore 30 ("microhole")
extending between the first and second ends 14, 16. A center of the
ferrule bore 30 defines an optical axis A.sub.1, and the first end
14 of the ferrule 12 defines a front end face 32 positioned at an
angle .phi. relative to the optical axis A.sub.1. The front end
face 32 is shown as being orthogonal to the optical axis A.sub.1 in
the embodiment of FIG. 1 such that the angle .phi. is 90.degree..
In other embodiments, the front end face 32 may be
non-orthogonal.
[0037] As shown in FIG. 1, an end portion of an optical fiber 40
may be inserted from a rear of the ferrule bore 30 and extended
until the optical fiber 40 exits an opening of the ferrule bore 30
on the front end face 32 of the ferrule 12. Thus, the optical fiber
40 protrudes past the front end face 32 by a distance H.sub.1
("protrusion height"). Details relating to the how the optical
fiber 40 may be inserted into and secured within the ferrule bore
32 will be described in greater detail below. In general, methods
may be used that advantageously provide a mechanical interface
between an inner surface of the ferrule bore 30 and an outer
surface of the optical fiber 40 before fusing the optical fiber 40
to the ferrule 12, thereby avoiding the need for a bonding agent
(e.g., epoxy).
[0038] The optical fiber 40 may be part of a fiber optic cable 42
upon which the fiber optic connector 10 is installed. As
schematically shown in FIG. 4, the end portion (noted with
reference number 44) of the optical fiber 40 is exposed from an
outer jacket 44 that surrounds and protects other portions of the
optical fiber 40. The end portion may represent part of a "bare"
optical fiber portion in that the end portion is not only exposed
from the outer jacket 44, but is also stripped or otherwise devoid
of a primary coating up to a transition interface 48. In other
words, and as shown in FIGS. 5 and 6, the optical fiber 40 includes
a bare optical fiber portion 50, which may comprise silica, and a
primary coating 52, which may comprise an acrylate polymer, within
the outer jacket 46, which may comprise a polyurethane acrylic
resin. The outer jacket 46 surrounds the optical fiber 40 (i.e.,
both the primary coating 52 and bare optical fiber portion 50)
until the transition interface 48 (FIG. 4), where both the primary
coating 52 and outer jacket 46 have been removed. Although the
primary coating 52 is shown as being removed from the entire length
of the optical fiber 40 extending from the outer jacket 46, in
alternative embodiments the primary coating 52 may cover some of
the length exposed from the outer jacket 46.
[0039] Referring back to FIG. 1, the second end portion 22 of the
ferrule holder 18 is received in the housing 24. A spring 60 may be
disposed around the second end portion 22 and configured to
interact with walls of the inner housing 24 to apply a biasing
force F.sub.S to the ferrule holder 18 (and ferrule 12).
Additionally, a lead-in tube 62 may extend from a rear end 64 of
the housing 24 to within the second end portion 22 of the ferrule
holder 18 to help guide the insertion of the optical fiber 40 into
the ferrule 12 during assembly (discussed below). An outer shroud
66 is positioned over the ferrule 12, ferrule holder 18, and
housing 24, with the overall configuration being such that the
front end face 32 of the ferrule 12 is configured to contact a
mating component (e.g., another fiber optic connector; not
shown).
[0040] In a manner not shown herein, the fiber optic cable 42 may
include one or more layers of material (e.g., a strength layer of
aramid yarn) that may be crimped onto the rear end 64 of the
housing 24. A crimp band may be provided for this purpose.
Additionally, a strain-relieving boot may be placed over the
crimped region and extend rearwardly to cover a portion of the
fiber optic cable 42. Variations of these aspects will be
appreciated by persons skilled in the design of fiber optic cable
assemblies. Again, the embodiment shown in FIG. 1 is merely an
example of a fiber optic connector that may be used in the methods
described below. The general overview has been provided simply to
facilitate discussion.
[0041] Now that the fiber optic connector 10 has been introduced to
facilitate discussion, exemplary methods of securing the optical
fiber 40 to the ferrule 12 will now be described. A high-level
description of one exemplary method for forming a mechanical
interface will first be provided, followed by a more detailed
description of each of the steps and variants thereof that may be
part of other exemplary methods. The mechanical interface
temporarily secures the optical fiber 40 to the ferrule 12.
Afterwards, a permanent attachment/connection may be formed by
fusing the optical ferrule 40 to the ferrule 12. A more detailed
description of aspects relating to such fusing will be provided
below following the description of aspects relating to forming the
mechanical interface.
[0042] To this end, as generally shown in FIGS. 7A-7D, one method
of securing the optical fiber 40 to the ferrule 12 first involves
providing the ferrule 12 and the optical fiber 40. Initially the
ferrule bore 30 may have a minimum bore diameter D.sub.B1 ("minimum
bore width") that is less than a maximum diameter D.sub.OF
("maximum fiber width") of the end portion 44 of the optical fiber
40. Prior to inserting the end portion 44 of the optical fiber 40
into the ferrule bore 30, the ferrule 12 is heated by an energy
source 70. The ferrule 12 experiences thermal expansion when heated
such that the ferrule bore 30 increases in diameter. Once the
temperature of the ferrule 12 reaches a threshold temperature, the
ferrule bore 30 increases to a minimum bore diameter D.sub.B2 that
is greater than the maximum diameter D.sub.OF of the end portion 44
of the optical fiber 40. As shown in FIG. 7C, the end portion 44 of
the optical fiber 40 may then be moved toward the second end 16 of
the ferrule 12 and inserted into the ferrule bore 30. Insertion
continues until the end portion 44 reaches or extends beyond the
front end face 32 of the ferrule 32. At this point, the ferrule 12
is cooled so that the ferrule bore 30 decreases in diameter.
Eventually the ferrule bore 30 decreases to a minimum bore diameter
D.sub.B3 (FIG. 7D) as the inner surface of the ferrule bore 30
constricts around the outer surface of the end portion 44 of the
optical fiber 40. The minimum bore diameter D.sub.B3 may be less
than a maximum diameter D.sub.F1 of the optical fiber 40 so that a
force F.sub.1 is applied by the ferrule 12 to the optical fiber 40,
thereby establishing a mechanical interface. In some embodiments,
the minimum bore diameter D.sub.B3 may be greater than the minimum
bore diameter D.sub.B3 but less than the minimum bore diameter
D.sub.B2.
[0043] Now referring to specific aspects of the above-described
method, the optical fiber 40 and ferrule 12 are initially provided
at a temperature below the threshold temperature. The threshold
temperature may be set above a normally expected temperature
operating range of the fiber optic connector 10. In some
embodiments, for example, the threshold temperature may be
100.degree. C. The dimensions and material properties of the
optical fiber 40 are such that the minimum bore diameter D.sub.B1
of the ferrule bore 30 is less than the maximum diameter D.sub.F1
of the end portion 44 of the optical fiber 40, as mentioned above,
when the ferrule 12 is below the threshold temperature.
[0044] In terms of heating the ferrule 12 to increase the minimum
bore diameter D.sub.B1, the energy source 70 is shown generically
in FIG. 7B because different embodiments may employ different
sources/techniques to cause thermal expansion of the ferrule 12. In
some embodiments, the energy source 70 may comprise at least one
laser. FIG. 8, for example, illustrates an embodiment where a laser
80 is used to irradiate the ferrule 12 with laser energy to cause
thermal expansion. The laser energy is delivered by a laser beam 82
emitted from the laser 80. Uniform or bulk heating of the ferrule
12 may be desired in some embodiments and provided by selecting an
appropriate combination of optical delivery properties of the laser
80, such as wavelength, power or fluence, duty cycle of pulses,
beam shape, beam focus, etc., as well as how the laser 80 is
oriented (i.e., angled), positioned, and/or moved relative to the
ferrule 12 (or vice-versa). One specific example of a suitable
laser is a carbon dioxide laser that operates at one or more
wavelengths in the range of 0.1 microns to 11 microns. Other types
of lasers are also possibilities.
[0045] In alternative embodiments, and as shown in FIG. 9, the
energy source may comprise an electrical heating source 90 of an
oven 92 into which the ferrule 12 is inserted. Once heated and
thermally expanded, the ferrule 12 is removed from the oven 92.
[0046] Another alternative is shown in FIG. 10, which illustrates
the energy source in the form of an electrical current source 100.
An electromagnet 102 is coupled to the electrical current source
100 and includes one or more coils 104 disposed around the ferrule
12. When the electrical current source 100 provides an alternating
current to the electromagnet 102, the coils 104 inductively heat
the ferrule 12. More specifically, the ferrule 12 may comprise
zirconia, or other materials, that provide some electrical
resistance to eddy currents induced by the electromagnet 102. The
electrical resistance results in heat being generated in the
ferrule 12.
[0047] In some embodiments, the optical fiber 40 may be heated in
addition to the ferrule 12. This may reduce the risk of thermal
shock to the ferrule 12 or optical fiber 40 when the two components
are later placed in contact. A common energy source (e.g., the
laser 80 of FIG. 8 or the electrical heating source 90 and oven 92
of FIG. 9) may be used to heat the optical fiber 40 and ferrule 12.
In such embodiments, however, the materials of the optical fiber 40
and ferrule 12 are selected so that a coefficient of thermal
expansion of the ferrule 12 is greater than a coefficient of
thermal expansion of the optical fiber 40. This allows the minimum
bore diameter D.sub.B1 of the ferrule bore 30 to increase in size
faster than the maximum fiber diameter D.sub.F1 under the same
heating conditions. The ferrule 12 may even have a coefficient of
thermal expansion at least 15 times greater than the optical fiber
40 in some embodiments.
[0048] Cooling the ferrule 12 to form the mechanical interface with
the optical fiber 40 may be achieved passively or actively.
Accordingly, in some embodiments, cooling may simply be a matter of
turning off or removing the energy source 70 (FIG. 7B) so that the
ferrule 12 is no longer heated. The ferrule 12 may then be allowed
to return to a temperature below the threshold temperature. No
powered devices (e.g., fans, pumps, etc.) are used to promote the
heat transfer. In other embodiments not shown herein, powered
devices may be used to provide active cooling. Regardless, and as
mentioned above, when the ferrule 12 cools back below the threshold
temperature, the ferrule bore 30 decreases to the minimum bore
diameter D.sub.B3 so as to be less than the maximum diameter
D.sub.F1 of the end portion 44 of the optical fiber 40. Cooling the
ferrule 12 a number of degrees (e.g., at least 5.degree.,
10.degree., 15.degree.) below the threshold temperature helps
ensure that the inner surface of the ferrule bore 30 forms the
mechanical interface with the entire outer surface of the end
portion 44 of the optical fiber 40 that is located within the
ferrule bore 30. For example, if the threshold temperature is
100.degree. C., the ferrule 12 (and optical fiber 40, if heated as
well) may be cooled to a temperature less than or equal to
95.degree. C.
[0049] The mechanical interface formed between the ferrule 12 and
optical fiber 40 facilitates one or more additional processing
steps that fuse the optical fiber 40 to the ferrule 12. Fusing
involves merging/melting/welding the optical fiber 40 and ferrule
12 together and may be accomplished by using one or more lasers to
irradiate the optical fiber 40 and ferrule 12 with laser energy. In
general, the materials of the optical fiber and ferrule are
irradiated with sufficient energy to transform into liquid states
so that the materials can blend together and later solidify to form
a single entity. By providing the mechanical interface between the
optical fiber and ferrule prior to fusing, gaps between the optical
fiber and ferrule are reduced or eliminated where the fusing is
desired. As a result, the need for molten material to flow from
nearby regions of the optical fiber and/or ferrule to fill gaps
during fusing is reduced or eliminated. This has the advantage of
helping preserve the geometries and spatial relationships that are
important for establishing effective optical couplings with mating
components.
[0050] The laser(s) used for fusing may be the same laser(s) used
to heat and thermally expand the ferrule 12 in some embodiments
(e.g., the embodiment of FIG. 8). Even further, the same laser(s)
may also be used to form an optical surface on the end portion 44
of the optical fiber 40 at a protrusion height H.sub.1 (FIG. 1)
within 50, 15, or even 10 microns of the front end face 32 of the
ferrule 12. The laser(s) may even be used to form such an optical
surface flush with the front end face 32. As can be appreciated,
however, at least one optical delivery property of the laser(s) may
be changed for the different processing steps to provide the
different result (i.e., fusing instead of heating/thermally
expanding, and forming an optical surface instead of fusing).
Exemplary optical delivery properties include, without limitation:
wavelength, power or fluence, duty cycle of pulses, beam shape, and
beam focus. How the laser(s) is/are oriented, positioned, and/or
moved relative to the ferrule 12 (or vice-versa) may also be
changed. One specific example of a suitable laser for fusing is a
carbon dioxide laser that operates at one or more wavelengths in
the range of 3 microns to 11 microns. Other types of lasers are
also possible.
[0051] With this in mind, FIG. 11 illustrates one example of how
the optical fiber 40 may be fused to the ferrule 12. The notch 26
(FIGS. 1 and 2) in the ferrule 12 is not shown to simplify matters.
Indeed, the notch 26 may not even be present in some embodiments.
As schematically shown in FIG. 11, a laser 110 may deliver laser
energy toward the ferrule 12 in any of various directions, as
represented by the arrows A in FIG. 11, including from nearly
parallel to the optical fiber 40 to perpendicular to the optical
fiber 40, or even beyond perpendicular to the optical fiber 40. The
ferrule 12 and optical fiber 40 may also be rotated in the
direction R and translated in the direction T as shown, so as to
fuse end portion 44 of the optical fiber 40 to the ferrule 12 along
at least 10%, 25%, or 50% of the length of the ferrule bore 30. In
some embodiments, the optical fiber 40 may even be fused to the
ferrule 12 along the entire length of the ferrule bore 30. In other
embodiments, the optical fiber 40 may only be fused to the ferrule
12 a locations L within the ferrule bore 30 that are at least a
distance d from the front end face 32. For example the optical
fiber 40 may only be fused to the ferrule 12 at locations L at
least 1 mm (or 2 mm, 5 mm, etc.) deep inside the ferrule bore 30
such that the distance d is at least 1 mm (or 2 mm, 5 mm, etc.).
The laser 100 may be moved relative to the optical fiber 40 and
ferrule 12, rather than moving the optical fiber 40 and ferrule 12
relative to the laser 100, to provide either or both the rotation
in the direction R and the translation in the direction T.
[0052] FIGS. 12 and 13 schematically illustrate another example of
how a laser 120 may be used to fuse the optical fiber 40 to the
ferrule 12. As shown in FIGS. 12 and 13, the laser 120 may emit a
laser beam B (only the outermost rays are represented) that has
been focused with a short focal length lens so to a have an extreme
convergence angle. The laser beam B is largely transmissive through
the ferrule 12, but develops enough intensity or energy density at
the center of the ferrule 12 to fuse the end portion 44 of the
optical fiber 40 to the ferrule 12. Both relative axial rotation R
and relative translation T may be used to perform a rapid helical
sweep of the ferrule 12 with the laser beam B. Such a sweeping
technique may facilitate fusing across the entire mechanical
interface formed between the optical fiber 40 and ferrule 12,
particularly when the ferrule 12 as a whole comprises largely
(i.e., greater than 75%), substantially (i.e., greater than 95%),
or entirely (i.e., 100%) fused silica, borosilicate, glass ceramic,
or the like. Ferrules comprised in this manner are considered to be
"non-composite ferrules" according to this disclosure.
[0053] On the other hand, processes or methods where a laser beam
approaches the front end face 32 of the ferrule 12 to irradiate the
ferrule 12 with laser energy may be more suited for embodiments
where the ferrule 12 comprises an inorganic composite material
having a material gradient (a "composite ferrule" according to this
disclosure). The composite material may, for example, have a
material gradient from at least 75% (or even further, at least 90%
or 100%) by volume of a first inorganic material to at least 75%
(or even further, at least 90% or 100%) by volume of a second
inorganic material in a radially inward direction of the ferrule
(i.e., radially inward relative to the optical axis A.sub.1). In
some embodiments, the first inorganic material may comprise or
consist of a ceramic, such as alumina and/or zirconia, while the
second inorganic material may comprise or consist of a glass or
glass material, such as silica. Alternatively or additionally, the
first inorganic material may have a fracture toughness of at least
1 MPam1/2 (or even further, at least 1.5 MPam1/2), and the second
inorganic material may have a softening point less than
1000.degree. C. (or even further, less than 900.degree. C.).
[0054] To illustrate these aspects in further detail, FIG. 14 is a
plot that shows an example of a material gradient 128 for the
ferrule 12. The vertical axis represents the percentage by volume
of the respective phase or material component of the ferrule 12,
with trace 130 representing the percentage of the first inorganic
material and trace 132 representing the percentage of the second
inorganic material. The horizontal axis represents the distance
along a radius of the ferrule 12, measured from the center of the
ferrule at radius 0 (i.e., the optical axis A.sub.1 in the
embodiments discussed above) to an outer radius r (FIG. 13). As
shown in FIG. 14, there are different regions of the plot that
correspond to different regions of ferrule 12. In a first region
134, which corresponds to an outer region of the ferrule 12, the
material of the ferrule 12 is 100% the first inorganic material. In
a second region 136, which corresponds to an inner region of the
ferrule 12 (i.e., proximate the ferrule bore 30), the material of
the ferrule 12 is 100% the second inorganic material. A third,
intermediate region 138 includes the material gradient, where the
percentages of the first inorganic material and second inorganic
material transition smoothly between their respective values in the
first and second regions 134, 136. Again, FIG. 14 is merely an
example, as the material gradient may be between different
percentages of the first and second inorganic materials in other
embodiments; between something other than 100% such that the
innermost and outermost regions of the ferrule 12 comprise
composite materials.
[0055] The length of the first, second, and third regions 134, 136,
138 may also vary in different embodiments. The third region 138
with the material gradient may, for example, extend along at least
1/10 (or at least 1/3, 1/2, etc.) of the length of the radius of
the ferrule 12. The plot in FIG. 12 shows the third region 138
extending along about 1/2 or more of the length of the horizontal
axis, which corresponds to about 1/2 or more of the length of the
radius r. Providing the gradual transition from the first inorganic
material to the second inorganic material over such a large region
of the ferrule 12 helps spread any stresses that may arise between
the first and second inorganic materials over the operating
temperature range of the ferrule 12. In other words, rather than
being concentrated in localized areas, such as at an interface
between two distinct layers of material, stresses may be spread
across the third region 138. This advantage also applies to
embodiments where the third region 138 only extends along 1/10 or
more of the length of the radius r (rather than 1/2 or more),
although possibly to a lesser extent.
[0056] In other contemplated embodiments, layers of composite
material having differing ratios of the first and second inorganic
materials may provide a stepped transition from an exterior of the
ferrule 12 to the ferrule bore 30. For each successive layer from
the exterior toward the ferrule bore 30, the percentage of the
second inorganic material may increase while the percentage of the
first material may decrease in a corresponding manner. Accordingly,
the outermost layer corresponds to the outer region of the ferrule
12 and has a ratio according to the percentages above (100%, 90%,
75%, etc., depending on the embodiment). The innermost layer
corresponds to the center of the ferrule, or more specifically the
inner surface of the ferrule bore 30, and has a ratio according to
the percentages above (100%, 90%, 75%, etc., depending on the
embodiment). Any number of discrete layers may be provided between
the outermost and innermost layers, bringing the total number of
discrete layers to three or more. Providing three or more discrete
layers, and especially five or more discrete layers, helps ensure
that the degree of change in coefficient of thermal expansion at
the interface/transition between adjoining layers does not result
stresses great enough crack the ferrule 12 or delaminate the layers
as the optical fiber 40 is fused to the ferrule 12.
[0057] Other ferrule constructions may be provided to facilitate
fusing the optical fiber 40 to the ferrule 12. For example, FIG. 15
illustrates a ferrule 210 that includes an interior 216 defining a
bore 212 configured to receive a waveguide, such as an optical
fiber 214. The ferrule 210 is graded or layered. The interior 216
of the graded or layered ferrule 210 includes a low-expansion
material, such as a material having a coefficient of thermal
expansion that is less than 40.times.10-7/.degree. C., preferably
less than 30.times.10-7/.degree. C. In some embodiments, the
interior 216 includes a boro-silicate or silica glass, preferably a
silica glass. The interior 216 may have an outer diameter 218 that
is greater than 200 microns, but in some embodiments, is less than
2.3 mm in diameter. For example, the interior 216 may have a
diameter between 300 microns and 1 mm in some embodiments, or even
between 300 microns and 600 microns in some embodiments.
[0058] The ferrule 210 further includes an outer region 220 and/or
layer (e.g., exterior 222 of the ferrule 210) that includes a
ceramic plus glass. In some such embodiments, the ceramic includes
zirconia, preferably tetragonal zirconia with the ceramic being
more than 40 volume percentage of the composition of the exterior
222 of the ferrule 210.
[0059] According to an exemplary embodiment, the interior 216 of
the ferrule 210 may be a redrawn glass rod (e.g., silica rod) with
an inner-diameter bore 212 (e.g., hole) of about 120-130 microns in
cross-sectional diameter. In some embodiments, one end is tapered
(not shown) from the outer diameter of the silica rod to the inner
hole, which may ease insertion of the optical fiber 214.
[0060] As previously mentioned, the ferrule 210 is graded between
the interior 216 and exterior 222. In some embodiments, a second
layer 226 of the ferrule 210 adjoining the interior 216 of the
ferrule 210 may include a layer of low-expansion glass,
glass/ceramic, or glass plus ceramic. The second layer 226 has a
higher coefficient of thermal expansion than the low-expansion
inner core (i.e., interior 216). According to an exemplary
embodiment, the ferrule 210 includes a third layer 228 of glass,
glass/ceramic, or glass plus ceramic having a coefficient of
thermal expansion that is greater than the second layer 226. In
some embodiments, the ferrule 210 may further include a fourth
layer 230 of higher-expansion glass, glass/ceramic, or glass plus
ceramic; and a fifth and outer layer 220 of still higher expansion
glass/ceramic or glass plus ceramic.
[0061] In some embodiments, a ferrule 210 for optical waveguides
includes a glass plus crystalline ceramic, where the thermal
expansion coefficient is graded in layers or continuously changes.
In some such embodiments, the thermal expansion coefficient changes
from less than 7.times.10-7/.degree. C. for material on the
interior 216 of the ferrule 210 to greater than
90.times.10-7/.degree. C. for material on the exterior 222 of the
ferrule 210. The thermal expansion coefficient for layers 216, 226,
228, 230, 220 of the ferrule 210 may increase in incrementally
greater amounts with distance from the interior 216 of the ferrule
210, or the thermal expansion coefficient material may
continuously, and smoothly increase with distance from the interior
216. In other embodiments, some intermediate layers or sections may
contrast the general trend, temporarily decreasing in coefficient
of expansion or staying the same with respect to distance from the
interior 216 of the ferrule 210. Such layers or sections, for
example, may serve other functions for the ferrule 210, such as to
facilitate laser light transmission or provide thermal barriers
with respect to heat transfer.
[0062] In general, the larger the grading layer or intermediate
expansion layer, the less stress there is in the body of the
ferrule 210. In some embodiments, the interior 216 of the ferrule
210 is silica, the exterior 222 is at least 40% crystalline
zirconia, and an intermediate expansion grading or layer 226 is
positioned therebetween. The intermediate expansion 226 grading or
layer may be greater than 20 microns thick, such as at least 100
microns. In other such embodiments, the ferrule 210 includes a
boro-silicate. In still other embodiments, the glass in the
intermediate grading or intermediate layer 216 includes a glass of
(in mole %) 59.08 SiO2, 13.33 B2O3, 9.37 Al2O3, 8.03 Na2O, 4.09
CaO, 1.28 Li2O, 1.64 K2O, 1.79 MgO, 1.37 ZrO2.
[0063] In some embodiments, material of the exterior 222 is greater
than 40% crystalline zirconia and also includes a glass of (in mole
%) 59.08 SiO2, 13.33 B2O3, 9.37 Al2O3, 8.03 Na2O, 4.09 CaO, 1.28
Li2O, 1.64 K2O, 1.79 MgO, 1.37 ZrO2. According to at least one
embodiment, the grading or layer 226 of the ferrule 210 is over
more than 20 microns in thickness and is located next to the
interior low-expansion core (i.e., interior 216) is comprised of
25% or more of a glass or glass-ceramic, such as including at least
one the families of Glass B (mole %): 60.0 SiO2, 20.0 Al2O3, 20.0
ZnO and Glass C (mole %): 59.0 SiO2, 19.6 Al2O3, 12.4 ZnO, 6.8
Li2O, 2.2 ZrO2.
[0064] In some embodiments, the interior 216 of the ferrule 210 is
formed by a low-expansion core that is at least 200 microns in
outer diameter 218. In some such embodiments, the core is at least
300 microns in outer diameter 218. In some embodiments, crystalline
ceramic material is in the exterior 222 of the ferrule 210. In some
of those embodiments, the crystalline ceramic material includes
zirconia, preferably zirconia that is mainly tetragonal. The
zirconia may be doped with a rare earth oxide, Y, Ca, Mg, In, or Sc
oxides and combinations thereof. The zirconia may also contain
stabilizing dopant aids of oxides of Ti or Sn and/or toughening
agents of oxides of Nb, Ta, W, and Mo. Some embodiments include a
layered or graded ferrule 210 where crystalline ceramic of the
exterior 222 is zirconia with 3 mole % or less yttria, with the
zirconia having less than 2.5 mole % yttria being more
preferred.
[0065] Although some of the examples below use cold pressing as a
shape forming method, there are a great variety of methods that can
be used for forming the graded or layered body. One of the most
useful of such methods includes pressure-less sintering. To reduce
stresses developed by the thermal expansion differences of
materials of the ferrule 210, low fabrication (sintering)
temperatures may be used. For example, processes where ferrules are
sintered at less than 1100.degree. C. are preferred, with less than
1000.degree. C. being more preferred, with 950.degree. C. being
even more preferred, with 850.degree. C. being still more
preferred.
[0066] In some contemplated embodiments, layered or graded
structures of a ferrule 210 as disclosed herein may be formed
directly form graded or layered powders. When sintering a pure
silica core, according to an exemplary embodiment, temperatures
over 1400.degree. C. may be used. However, such temperatures may
cause de-vitrification issues with some composition combinations
used for the intermediate layers 230, 228, 226. As such, it is
preferred to sinter the ferrule 210 around a pre-formed
low-expansion core rod (e.g., inner layer 216) having a central
bore 212 hole. The central core rod may be redrawn with an accurate
central bore if the low expansion core is a glass. Silica and
boro-silicates are particularly amenable to this re-draw
process.
[0067] For ease of processing, the crystalline ceramic powders can
be used in the form of agglomerates (see agglomerates 312 as shown
in FIG. 16), such as may be produced via a spray drying process.
With some crystalline ceramic compositions, there may be improved
performance by pre-sintering the agglomerates, particles, grains
etc. (prior to sintering the ferrule 110) to achieve the desired
grain size for the properties of interest. For instance,
pre-sintering zirconia agglomerates in temperatures between 1250
and 1700.degree. C., preferably between 1300 and 1600 C, may
provide near-spherical granules that are nearly pore free, with
mostly tetragonal phase zirconia. For example, with such a process,
the grains size is large enough to allow some transformation to
monoclinic zirconia, allowing the possibility of some
transformation toughening.
[0068] According to another exemplary embodiment, if a
low-expansion core cane (e.g., interior 216) is being made by
redraw, layers 226, 228, 230 may be added and/or gradient may be
provided using coating cups, drying regions, and/or sintering
regions on the end of the draw, in a manner similar to applying a
protective polymer coating to optical waveguides. In some such
embodiments, there can be a coating cup and drying station for each
layer, and if the layer composition can sinter rapidly, there may
be two or more coating stations with drying and sintering regions,
where the rod or cane is drawn through continuously.
[0069] According to an exemplary embodiment, extrusion may be a
particularly useful shape forming method for elongate objects, such
as those with constant cross-sections. Ram extrusion using a billet
of material, where the billet contains the composition gradient or
the differing composition layers, may be used to form the complete
unfired ferrule body or a graded or layered tube where a core rod
of low expansion glass is also used, preferably inserted prior to
sintering.
[0070] According to some such embodiments, co-extrusion, using more
than two feed streams, may be utilized and can give better results
than billet/ram extrusion. For example, the entire structure may be
co-extruded or several layers can be co-extruded and a dense core
rod inserted therein. In some alternate embodiments, tubes of
various diameters and compositions can be extruded singly,
assembled into layered/graded rods or tubes, perhaps with a
pressing operation after assembly to insure knitted interfaces.
[0071] According to other embodiments, cold-pressing, uniaxial, dry
bag quasi-iso-static, wet bag iso-static methods may be used for
forming the ferrule 210. For a dry wet bag or even a uniaxial
pressing operation, there may be a series of concentric funnels
that can fill the bag or die simultaneously, and then only one
pressing operation for the ferrule 210. As shown in the examples
below, powders may be pressed and sintered around a dense core rod.
Repeated pressing operations are contemplated, with a new
composition being built up around the interior body to create
layers and gradients. Such pressing operations may be done around a
dense core rod, but need not be limited to concentric cylinders of
differing compositions and/or thermal expansion coefficients.
Assembly of a graded or layered tube around a glass core may be
done via a second pressing operation to increase contact between
the core and the powder tube. With some such methods too, tubes of
various diameters and compositions can be pressed singly, assembled
into layered/graded rods or tubes, perhaps with a pressing
operation after assembly to insure knitted interfaces.
[0072] In some contemplated embodiments, the graded or layered
ferrule 210 has a significant amount of glass in some or all areas
of the ferrule 210, and does not include a separate central core of
glass. Further, the viscosity/composition of the glass may be
adjusted (via material selection) to give similar viscosities for
the various glass, glass-ceramic, glass plus ceramic layers or
gradient, and then a large graded or layered blank may be built
before re-drawing all or part of the ferrule structure. Redrawing a
tube may require careful control of the pressure or vacuum in the
central bore hole during the re-draw process.
[0073] In other contemplated embodiments, electrostatic methods may
be used for providing graded or layered rod shapes. For example,
dry or wet powder can be electrically charged, strong thin gatherer
wire filament may be oppositely charged, or a core cane/rod can be
coated to make the core cane/rod slightly conductive, and a layered
or graded ferrule pre-form can be made. Hollow graded or layered
tubes can be made and assembled around an interior glass core. The
core rod can be drawn continuously through different powder
chambers or different powders may be introduced to a single
chamber. For example, metallic pre-forms with a plethora of rod
"gatherer" shapes can be used.
[0074] In some contemplated embodiments, slip casting methods can
be used for graded or layered rod shapes. Powder can be dispersed
in a fluid usually via surfactants and suitable salt, acid, base
adjustment to the carrier fluid, and the powder deposited in a
porous mold. The layered or graded ferrule pre form can be made by
sequential removal then additions of fluids with differing powder
compositions. A fluid can be delivered to the mold via a tube and
the composition of the fluid and powder in the tube varied with
time. Hollow graded or layered tubes can be made and assembled
around an interior glass core. Pressure slip casting can also be
practiced.
[0075] In still other contemplated embodiments, electrophoretic
methods may be used to provide graded or layered rod shapes. For
example, powder can be electrically charged, usually via
surfactants and suitable salt, acid, base adjustment to the carrier
fluid. The powder may then be deposited on a strong thin gatherer
wire filament oppositely charged, or a core cane/rod coated to make
the core cane/rod at least slightly conductive, and the layered or
graded ferrule pre-form can be made. Hollow graded or layered tubes
can be made and assembled around an interior glass core. The core
rod can be drawn continuously through different fluid chambers or
different powders/fluids may be introduced to a single chamber.
Metallic pre-forms with a plethora of rod "gatherer" shapes can be
used.
[0076] Single-composition ferrules are typically made by injection
molding, sintering, and machining. Some embodiments may involve
injection molding a core powder, then sequentially taking the part
and putting the part into larger and larger dies, and thereby
injection molding more layers around the original core. To maintain
the sample of the first core (e.g., interior 216) and layers 226,
228, 230, each succeeding layer may need a lower temperature
carrier polymer.
[0077] For at least some of the layers, such as the outer
crystalline ceramic containing layers 220 or layers forming the
gradient, layers or regions with a porosity or a porosity and
composition gradient/layers can be arranged as a pre-form and then
infiltrated with glass. The infiltration can be driven via
capillary forces, or an external pressure can be used.
Additionally, the ferrule pre-form may be covered with a gas
impermeable glass, and hot iso-static presses may be used.
[0078] According to an exemplary embodiment, a combined technique
of pull-trusion with either a billet or multiple feed die can be
utilized. With a strong core rod, the rod may be mounted on a reel,
the real put into a pressure vessel, and the interior rod fed into
a billet or multi-feed die and/or extrusion feed pressure chamber,
with a seal between the reel pressure chamber and the extrusion
feed chamber. With pressures in the two chambers balanced, the core
rod may be pulled through an extrusion die while the layered or
graded ferrule powder is extruded onto it. A gas or hydraulic
pressure can be fed into the reel pressure chamber to prevent
hydraulic pressure to prevent extrusion batch back flow.
[0079] Another extrusion method includes use a carousel form to
hold a core cane or inner core region, and a tube of one layer
extruded onto the inner core or rod. Upon heating and/or drying,
the outside tube and/or layer will shrink. Part or even the entire
carousel may be moved to a second extruder where another, larger
layer can be extruded over the previous material. This sequence may
be repeated until the final gradation and/or number of layers is
finished.
[0080] According to another exemplary embodiment, a layered and
gradient composition for ferrules 210 may be made by a
repeated-dipping method (conceptually similar to 17th century
candle making processes). For example, using a thin "bait" fiber or
a core rod, and repeatedly dipping the same into a molten slurry of
powder and polymer, the layers or gradient is constructed. To
maintain the sample of the first core and layers, each succeeding
layer may have a lower temperature carrier polymer.
[0081] The following examples are provided for context. In some
cases, examples below have porosity in layers 226, 228, 230 of the
ferrule 210 materials. For strength reasons, and for mechanical
reliability and wear concerns, the exterior surface 222 and/or
region 220 of the ferrule 210 has the fewest (i.e., a minimum of)
large pores relative to the rest of the ferrule 210, which can be
controlled through use of binders and plasticizers to achieve
better powder packing in some of the above-disclosed processes and
to achieve better grading of the size distribution of the powders,
and through use of bi- and tri-modal powders, where the smaller
powders "fit" into the interstices of the larger powders. Further,
porosity can be reduced by hot iso-static pressing. The hot
isostatic pressing may work particularly well when the temperature
of the pressing is near that of the sintering, such as within
200.degree. C. When the ferrule 210 is sintered to a closed
porosity, the ferrule material itself may support the pressure to
remove the porosity. The sintering and pressing can be done in a
single thermal cycle with a hot iso-pressing furnace. If there is
open porosity in the ferrule 210, then the surface should be made
gas impermeable to densify the ferrule 210, which can be
accomplished by providing a dense outer coating of glass or metal.
For example, in the 700 to 1300.degree. C. range, some ferrous
metals are applicable and can be acquired in thin sheets. Numerous
ferrules or a long length of numerous ferrules can be spaced on a
sheet of material (perhaps with depression for the ferrules), with
a second sheet layered on top and sealed, with the air being
evacuated. The ferrules or multi ferrule rods can then be hot
iso-statically pressed. Pressures at or below 30 kpsi are preferred
and cycle times of less than 12 hours are preferred.
EXAMPLES
[0082] Three different zirconia composition were used and three
different glass, glass-ceramic compositions where used. The
zirconia was purchased from Tosoh Chemical Company, Japan and were
TZ 0Y, zirconia without any dopant; TZ2Y, zirconia-2 mole % yttria;
and TZ3Y, zirconia with 3 mole % yttria. A medium thermal-expansion
(e.g., about 70.times.10.sup.-7.+-.20.times.10.sup.-7/.degree. C.
expansion coefficient), low-temperature sintering glass, glass A
(mole %): 59.08 SiO.sub.2, 13.33 B.sub.2O.sub.3, 9.37
Al.sub.2O.sub.3, 8.03 Na.sub.2O, 4.09 CaO, 1.28 Li.sub.2O, 1.64
K.sub.2O, 1.79 MgO, 1.37 ZrO.sub.2 and two low-expansion,
glass-ceramics (e.g., having an approximately 0 to
10.times.10.sup.-7/.degree. C. expansion coefficient), Glass B
(mole %): 60.0 SiO.sub.2, 20.0 Al.sub.2O.sub.3, 20.0 ZnO and Glass
C (mole %): 59.0 SiO.sub.2, 19.6 Al.sub.2O.sub.3, 12.4 ZnO, 6.8
Li.sub.2O, 2.2 ZrO.sub.2 were used. Silica "rods" of about 350-400
microns in diameter and 5.5.times.10.sup.-7/.degree. C. expansion
coefficient were also used. The silica "rods" were made by
re-drawing a silica boule and can be made with an accurate inner
diameter (bore) of about 126 micron.
[0083] As a guide for experimentation a simple semi-analytic stress
model was developed for two- to five-layer structures of
infinite-length, cylindrical, elastic structures with the outer
layer being about 2.5 mm in outer diameter, as shown in FIGS.
18-21. The model focused on the circumferential (tensile) stress
component and allowed for different thermal expansion coefficients,
Young's elastic moduli, Poisson's ratios, and layer numbers and
thicknesses. All the layers were assumed to be hollow cylinders,
except for the inner layer which was a solid cylinder, and all the
cylinders were concentric.
[0084] Referring once more to FIG. 15, a five-layer ferrule 210
includes a silica interior 216, a layer of a low-expansion glass
(e.g., silica core; lower thermal expansion coefficient than the
other layers); a layer of glass-ceramic 226 next to the silica core
216; an intermediate thermal expansion coefficient layer of glass
228, a higher thermal expansion glass plus zirconia layer 230, and
a higher-still expansion layer 220 of glass plus zirconia.
According to an exemplary embodiment, the ferrule 210 includes more
than two layers, where each of the layers is formed from a material
having a higher coefficient of thermal expansion than the adjacent
interior layer, and where the material of the innermost layer 216
has the lowest coefficient of thermal expansion.
Example 1
[0085] Glass A was melted then ground and milled into powder, with
the median powder particle size being between 3 to 7 microns; where
Glass A is a low-temperature sintering glass, including (mole %):
59.08 SiO.sub.2, 13.33 B.sub.2O.sub.3, 9.37 Al.sub.2O.sub.3, 8.03
Na.sub.2O, 4.09 CaO, 1.28 Li.sub.2O, 1.64 K.sub.2O, 1.79 MgO, 1.37
ZrO.sub.2. Agglomerates of zirconia-3 mole % yttria where
pre-sintered at 1300.degree. C. in air for 2 hours. Mixed
compositions of zirconia-3 mole % yttria pre-sintered agglomerates
were mixed with 50 volume %, 62.5 volume %, and 75 volume % Glass
A.
[0086] Thin layers of 100% Glass A, 75% Glass A, 62.5% Glass A, and
50% Glass A were spread in a steel bar die and uni-axially pressed.
The bar pre-form was placed in a latex iso-pressing bag, the air
was removed by a vacuum pump and the bag was sealed. The bar was
cold iso-statically pressed to about 25 kpsi. The pressed bar was
placed on coarse alumina "setter" sand in an alumina sagger box and
sintered at 900.degree. C. in air for 4 hours.
[0087] The bar was cut, polished, and examined by scanning electron
microscope SEM. FIG. 16 shows the cross-section structure, with the
bar intact. More specifically, FIG. 16 shows a SEM micrograph of
four sintered layers 314, 316, 318, 320.
Example 2
[0088] Glass-ceramic B was melted then ground and milled into
powder, with the median powder particle size being between 3 to 7
microns; where Glass B includes (mole %): 60.0 SiO.sub.2, 20.0
Al.sub.2O.sub.3, 20.0 ZnO. Agglomerates 212 of zirconia-3 mole %
yttria where pre sintered at 1550.degree. C. in air for 2 hours.
Mixed compositions of zirconia-3 mole % yttria pre sintered
agglomerates 312 were mixed with 50 volume % and 75 volume % Glass
A. Further, Glass A and glass-ceramic B (i.e., Glass B) were mixed
in a 50-50% ratio.
[0089] Thin layers of the mixture of 50% Glass A and 50%
glass-ceramic B, 100% Glass A, 75% Glass A and 25% zirconia 3 mole
% yttria, and 50% glass (e.g., Glass A) plus 50% zirconia-3 mole %
yttria were spread in a steel bar die and uni-axially pressed. The
bar pre-form was placed in a latex iso-pressing bag, air was
removed by a vacuum pump, and the bag was sealed. The bar was cold
iso-statically pressed to about 25 kpsi.
[0090] The pressed bars were placed on coarse alumina "setter" sand
in an alumina sagger box and sintered at 800.degree. C. or
900.degree. C. in air for 4 hours. The bars were intact and graded
from a low-expansion glass ceramic of between about
3.times.10.sup.-6 to 4.times.10.sup.-6/.degree. C. to a
high-expansion glass plus ceramic of about
9.5.times.10.sup.-6/.degree. C., where the bars across this
gradient were intact.
Example 3
[0091] Glass A and glass-ceramic B where mixed in a 50-50% ratio. A
layer of the mixture of 50% glass A and 50% glass-ceramic B was
spread in a steel bar die, a cleaned silica "rod" of between about
350-400 microns in diameter was placed in the die and a second
layer of powder was placed on top and uni-axially pressed. The bar
pre-form was placed in a latex iso-pressing bag, the air was
removed by a vacuum pump, and the bag was sealed. The bar was cold
iso-statically pressed to about 25 kpsi. The pressed bar was placed
on coarse alumina "setter" sand in an alumina sagger box and
sintered at about 800.degree. C. or 900.degree. C. in air for 4
hours. The bars were intact cross-sectioned and polished and
examined by SEM.
[0092] FIG. 17 shows the interface 412 of structure 410 between the
silica 414 and the sintered Glass A plus glass-ceramic B 316. No
de-vitrification was found at the silica interface 412 and no
fracture was found in the matrix sintered glass. The bonding is
very good. X-ray diffraction showed a pattern of the 50-50% Glass A
and glass-ceramic B fired at 900.degree. C. 2 hr. air, having
several different crystalline phases, Virgilite, Gahnite, Willemite
and Albite and glassy halos.
Example 4
[0093] Referring to FIGS. 18 and 19, using the semi-analytic stress
model, circumferential stresses in five-layer ferrules were
calculated. Table I below shows values used in the stress model.
Other than for the silica interior, the Poisson's ratio was
estimated to be 0.3, and Young's elastic modulus and thermal
expansion coefficient were treated as simple linear interpolations
between the end members. Layer 1 (412) is silica, layer 2 (414) is
a 50-50% mix of Glass A and glass-ceramic B, layer 3 (416) is 100%
Glass A, layer 4 (418) is 25 volume % zirconia-3 mole % yttria plus
75 volume % Glass A, and layer 5 (420) is 50 volume % zirconia-3
mole % yttria plus 50 volume % Glass A.
TABLE-US-00001 TABLE I Young's elastic Thermal Layer outer modulus
expansion radii Layer # GPa Poisson's ratio /.degree. C. mm 1 72.9
0.14 5.5 .times. 10.sup.-7 0.19 2 73 0.3 3.5 .times. 10.sup.-6 0.4
3 73 0.3 7 .times. 10.sup.-6 0.6 4 107 0.3 8.25 .times. 10.sup.-6
0.8 5 140 0.3 9.5 .times. 10.sup.-6 1.25
[0094] FIG. 18 shows the approximate circumferential stress
distribution 510 through the layers 512, 514, 516, 518, 520,
assuming the five-layer body was sintered at 800.degree. C. and
cooled to 0.degree. C., with no stress relaxation. As can be seen
from FIG. 18, the tensile stresses are moderately high at the
interface 522 between the fourth and fifth layers 518, 520, almost
300 MPa, but are manageable for a fiber optic connector.
[0095] The semi-analytic stress model was again used for a second
five-layer structure, where layer 1 (612; FIG. 19) is silica, layer
2 (614) is 50-50% mix of Glass A and glass-ceramic B, layer 3 (616)
is 100% Glass A, layer 4 (618) is 45 volume % zirconia-3 mole %
yttria plus 55% Glass A, and layer 5 (620) is 90% zirconia-3 mole %
yttria plus the remaining 10% being Glass A.
[0096] FIG. 19 shows the approximate circumferential stress
distribution 610 through the layers 612, 614, 616, 618, 620,
assuming the five-layer body was sintered at 800.degree. C. and
cooled to 0.degree. C., with no stress relaxation. Table II below
contains the relevant estimated properties. As can be seen, the
stresses are higher than the first case (shown in FIG. 19) due to
the larger thermal expansion difference and the higher elastic
modulus. The highest tensile stress is at the interface 622 between
the fourth and fifth layers 618, 620, about 550 MPa, but is still
manageable for a fiber optic connector.
[0097] The stresses shown on the graph of FIG. 19 are approximant
for several reasons. First, real-world interfaces are not
mathematically sharp, there is a jumble of composition visible in
the SEM micrographs along the interface between two compositions,
which will smooth the sharp stress peaks somewhat. Secondly, the
various composition layers are modeled as materials with uniform
thermal expansion and elastic properties, which is not the case for
the real-world materials having a combination of ceramic particles
(agglomerates) and glass. The stresses in the glass near the
ceramic particles and agglomerates is not uniform and the macro
stresses are overlaid upon the micro-thermal expansion
stresses.
TABLE-US-00002 TABLE II Young's elastic Thermal Layer outer modulus
expansion radii Layer # GPa Poisson's ratio /.degree. C. mm 1 72.9
0.14 5.5 .times. 10.sup.-7 0.19 2 73 0.3 3.5 .times. 10.sup.-6 0.4
3 73 0.3 7 .times. 10.sup.-6 0.6 4 134 0.3 9.4 .times. 10.sup.-6
0.8 5 196 0.3 11.5 .times. 10.sup.-6 1.25
Example I-z
[0098] Referring to FIGS. 20 and 21, using the same semi-analytic
stress model, the circumferential stresses in a 2-layer ferrule
were calculated for comparison and contextual purposes. Table III
below shows values entered into the stress model. The first layer
712 was assumed to be silica. Poisson's ratio was estimated to be
0.3 for the second layer 714, and the Young's elastic modulus and
the thermal expansion coefficient are that of 100% zirconia-3 mole
% yttria.
TABLE-US-00003 TABLE III Young's elastic Thermal modulus expansion
Layer outer radii Layer # GPa Poisson's ratio /.degree. C. mm 1
72.9 0.14 5.5 .times. 10.sup.-7 1.15 2 210 0.3 12 .times. 10.sup.-6
1.25
[0099] FIG. 20 shows the approximate circumferential stress
distribution 710 through the layers 712, 714, assuming the 2-layer
body was sintered at 1500.degree. C. and cooled to 0.degree. C.,
with no stress relaxation. As can be seen, the tensile stresses are
extremely high at the interface 716 between the two layers 712,
716, greater than 4000 MPa, which may cause a composite ferrule to
shatter.
Example II-z
[0100] Using the semi-analytic stress model once again,
circumferential stresses in a 2-layer ferrule were calculated.
Table IV below shows values entered into the approximate stress
model. The first layer 812 was assumed to be silica. The Poisson's
ratio was estimated to be 0.3 for the second layer 814, and the
Young's elastic modulus and the thermal expansion coefficient are
that of 100% zirconia-3 mole % yttria. With this second two-layer
model, instead of a thin coating, the zirconia outer layer 814 was
substantially thicker.
[0101] FIG. 21 shows the approximate circumferential stress
distribution 810, assuming the 2-layer body was sintered at
1500.degree. C. and cooled to 0.degree. C., with no stress
relaxation. As can be seen, the tensile stresses are extremely high
at the interface 816 between the two layers 812, 814, greater than
about 1800 MPa and the compressive stress on the silica interior is
very high, over 1000 MPa. A composite ferrule made this way may
shatter.
TABLE-US-00004 TABLE IV Young's elastic Thermal modulus expansion
Layer outer radii Layer # GPa Poisson's ratio /.degree. C. mm 1
72.9 0.14 5.5 .times. 10.sup.-7 0.6 2 210 0.3 12 .times. 10.sup.-6
1.25
Example 5
[0102] Zirconia-3 mole % yttria pre-sintered agglomerates 912 were
mixed with 37.5 volume % Glass A 914. The mixed powder was spread
in a steel die and uni-axially pressed. The sample pre-form was
placed in a latex iso-pressing bag, the air was removed by a vacuum
pump, and the bag was sealed. The sample was cold iso-statically
pressed to about 25 kpsi. The pressed sample was placed on coarse
alumina "setter" sand in an alumina sagger box and sintered at
900.degree. C. in air for 4 hours.
[0103] The sample 910 was cut, polished and examined by SEM. FIGS.
22 and 23 show the cross-section microstructure of 62.5% zirconia
agglomerates plus 37.5% Glass A.
Example 6
[0104] Commercial optical waveguide ferrules including zirconia may
be toughened via phase transformation toughening. However, when
materials for ferrule disclosed herein are sintered at temperatures
below about 1250.degree. C., the phases and grain size may not
develop sufficiently to allow for transformation toughening.
Furthermore, having significant glass as part of the ferrule
composition can change the nano stresses at the grain boundary,
which appear to play a role in nucleation of monoclinic zirconia
under an external stress field.
[0105] To facilitate transformation toughening with materials
disclosed herein, a survey of agglomerate pre-sintering
temperatures and zirconia yttria dopant levels was performed.
Zirconia compositions were used without pre-sintering or with
pre-sintering of the agglomerates at 1300.degree. C. to
1550.degree. C. for two hours in air. The zirconia types tested
included TZ0Y, zirconia without any dopant, TZ2Y, zirconia-2 mole %
yttria, and TZ3Y, zirconia with 3 mole % yttria. The pre-sintered
agglomerates were mixed with 50 volume % Glass A. The mixed powder
was spread in a steel die and uni-axially pressed. The sample
pre-form was placed in a latex iso-pressing bag, the air was
removed by a vacuum pump, and the bag was sealed. The sample was
cold iso-statically pressed to about 25 kpsi. The pressed sample
was placed on coarse alumina "setter" sand in an alumina sagger box
and sintered at about 800-900.degree. C. in air for 4 hours. 2.5 cm
square cross-section bars, about 6 inches in length, were pressed
and sintered. The samples were machined into chevron notched short
bar KIC specimens and room temperature KIC measured. The samples
were polished and examined by SEM and X-ray diffraction showed
phases in the samples.
[0106] Table V below summarizes the testing, and FIGS. 24-30 show
the results. FIG. 24 includes an SEM micrograph 910 of 2Y ZrO.sub.2
(1012) pre-sintered at 1500.degree. C. in 50 volume % Glass A
(1014) sintered at 900.degree. C. with KIC about 1.8 MPa m.sup.1/2.
FIG. 25 includes an SEM 1110 of 0Y ZrO.sub.2 (1112) in 50% Glass A
(1114) sintered 900.degree. C. with KIC about 1.3 MPa m.sup.1/2.
FIG. 26 includes an SEM 1210 of 3Y ZrO.sub.2 (1212) pre-sintered at
1550.degree. C. in 50% Glass A (1214) sintered 900.degree. C. with
KIC about 1.28 MPa m.sup.1/2. FIG. 27 includes an SEM 1310 of 3Y
ZrO.sub.2 (1312) pre-sintered at 1400.degree. C. in 50% Glass A
(1314). FIGS. 28-30 include SEM 1410 of 3Y ZrO.sub.2 (1412)
pre-sintered at 1300.degree. C. plus 50% Glass A (1414) sintered
900.degree. C. with KIC about 1.6 MPa m.sup.1/2.
TABLE-US-00005 TABLE V Zirconia Yttria pre-sinter Sintering
Fracture level in temper- Temper- Mono- toughness Zirconia Compo-
ature ature clinic KIC sample Mole % sition .degree. C. .degree. C.
level MPa(m).sup.1/2 alpha 0 1500 900 high 1.3 beta 2 1500 900
medium 1.8 gamma 3 1550 900 low 1.3 delta 3 1400 900 low -- Eta 3
1300 900 Very 1.6 low
[0107] It was found that agglomerates that were not pre-sintered,
when sintered with 50 volume % Glass A at about 800-900.degree. C.
showed no sign of transformation toughening. Pre-sintered TZ0Y
resulted in monoclinic zirconia and a fairly low KIC. Pre-sintered
TZ3Y showed tetragonal zirconia with only a low amount of
monoclinic in the x-ray pattern. TZ2Y pre sintered at 1500.degree.
C. showed a medium amount of monoclinic zirconia and an improved
toughness, 1.8 MPa (m).sup.1/2. Accordingly, the preferred amount
of yttria dopant in the zirconia is above 0 but 3 vol. % or lower
for some such embodiments. As shown in FIGS. 28-30, the SEM
micrographs 1410 show that sintering the loose agglomerates 1412
results in porous agglomerates 1412 at 1300.degree. C. and
1400.degree. C.
[0108] Referring now to FIG. 31, in some embodiments a multi-fiber
ferrule 1510 is manufactured and used according to the above
disclosure. Accordingly, in some such embodiments, the multi-fiber
ferrule 1510 includes a low-expansion material 1512 (e.g., glass)
coupled to an interior thereof and having a bore(s) 1514 defined
therein, a higher-expansion material 1516 (e.g., zirconia) on the
exterior of the ferrule 1510, and one or more graded transition
layers 1518, 1520 therebetween, as disclosed herein. The interior
1512 may include more than one bore 1514 to receive multiple
optical fibers 1522, where the low-expansion material 1512 forming
each bore 1514 may be connected or separated into isolated
bore-forming tubes, partitioned by the one or more transition
layers.
[0109] As shown in FIG. 31, each bore 1514 supports an optical
fiber 1522, where the bore 1514 is formed in a first material 1512
(e.g., glass, silica). The first material 1512 is surrounded by a
second material 1518 (e.g., porous inorganic material), which is
itself surrounded by a third material 1516 (e.g., typical zirconia
ferrule materials). The second material 1518 may provide
stress-isolation having higher porosity and/or lower elastic
modulus relative to the first 1512 and third materials 1516, as
further disclosed above with regard to other embodiments. In some
embodiments, the ferrule 1510 includes additional intermediate
layers 1518, 1520 between the bore 1514 and exterior 1516, which
provided a graded transition with respect to coefficient of thermal
expansion, modulus of elasticity, and/or other parameters, whereby
stresses are disrupted and/or distributed to reduce peak stresses.
The multi-fiber ferrule 1510 may support two, four, eight, twelve,
sixteen, twenty-four, thirty-two, or other numbers of optical
fibers 1522. In some embodiments, the multi-fiber ferrule 1510 is
rectilinear, and the end face 1524 is generally rectangular.
[0110] It was mentioned above how the same laser(s) used to
thermally expand the ferrule and/or fuse the optical fiber to the
ferrule may additionally be used to form an optical surface on an
end portion of the optical fiber. To this end, the laser or laser
may be considered to be part of a laser cleaving system. Laser
cleaving steps may be performed before fusing the optical fiber to
the ferrule or afterwards. Indeed, unless otherwise expressly
stated, it is in no way intended that any method set forth herein
be construed as requiring that steps be performed in a specific
order. Accordingly, where a method claim below does not actually
recite an order to be followed by its steps or it is not otherwise
specifically stated in the claims below or description above that
the steps are to be limited to a specific order, it is no way
intended that any particular order be inferred.
[0111] It will be apparent to those skilled in the art that
additional modifications and variations can be made without
departing from the spirit or scope of the claims below. For
example, although ferrules comprising a ceramic material and
optical fibers comprising silica are mentioned above, some claims
may not be limited to these materials. The methods described above
may also be applicable to plastic ferrules and optical fibers.
Other modifications, combinations, sub-combinations, and variations
of the disclosed embodiments may occur to persons skilled in the
art, yet still fall within the scope of the claims below.
* * * * *